WASHINGTON, Aug 28 (Reuters) - The worst ever outbreak of the Ebola disease is likely to lead to sharply lower growth in Guinea, Liberia and Sierra Leone and raise financing needs in all three West African countries, an IMF spokesman said on Thursday.

At least 1,500 people have died of the deadly hemorrhagic virus since it was detected in the remote jungles of southeast Guinea in March and spread quickly to neighboring Liberia and Sierra Leone. Five people have also died in Nigeria.

"The Ebola outbreak is having an acute macroeconomic and social impact on three already fragile countries in West Africa," IMF spokesman Gerry Rice told reporters.

"We are actively working with all three countries to prepare a preliminary economic assessment of the impact of the Ebola crisis, and additional financing support that may be required."

All three countries are already getting IMF loans under the extended credit facility, a longer-term IMF program available for poor countries with protracted balance of payments problems.

Guinea has a three-year, $200 million IMF program, Liberia is getting about $80 million over three years, and Sierra Leone has a three-year IMF program of about $96 million. (Reporting by Anna Yukhananov; Editing by Chizu Nomiyama and Jonathan Oatis)